1. Field of the Invention
The present invention relates generally to improvements in digital optical processing apparatus. More particularly, the present invention relates to apparatus for maintaining image definition and intensity throughout a multiple step parallel optical digital data processing operation.
2. Description of the Prior Art
In commonly assigned U.S. Pat. application Ser. No. 415,584 of Peter Nisenson, filed on Nov. 14, 1973, and entitled PARALLEL DIGITAL DATA PROCESSING SYSTEM, a parallel optical digital processing system is described wherein digital data is directed through an optical circuit and subjected to the standard logical manipulations of ANDing, ORing, shifting and inverting so as to enable the subject matter represented by the digital data to be processed in some desired manner. In an operative embodiment of the system, the digital data is transmitted through the circuit in the form of optical images consisting of two-dimensional arrays of light and dark areas representing binary ones and zeros, respectively. The circuit itself consists of a large number of electro-optic photosensitive storage devices coupled together by means of a variety of standard optical components such as mirrors, lenses and the like and responsive to the image arrays applied to them to establish internal electric fields representative of the intensities of the different bits of the arrays. By proper control over the circuit and the storage devices, one or more image arrays may be directed through the circuit along prescribed paths to enable the desired processing operations to be carried out.
In a typical processing operation, it is frequently necessary to read image arrays into and out of a large number of these storage devices, and, because of the need for these many iterations, some problems have arisen.
Specifically, it has been found that each time an image array is read into and out of a storage device, some degradation in the quality of the image results, and, after a series of iterations have been performed, deterioration can reach a point that errors may arise in the processing operation. This image deterioration is caused by several factors which will be described in some detail hereinafter, but basically it can be attributed to inherent non-uniformities in the intensity distribution of the light beams used to read data into and out of the storage devices, diffraction effects and system noise. The overall effect of these factors are to cause originally square image bits which make up the image array to assume non-uniform Gaussian shapes, to cause adjacent data bits to tend to overlap one another, and generally to reduce the overall intensity of the image. Put another way, in the operation of the processing system, the originally square bits of binary image data gradually lose their digital qualities and become more analog in nature with variations from point to point over the area of the data bit. This is obviously not a desirable condition in a digital system and makes accurate processing more difficult to obtain especially in long and detailed processing applications.